Low-if transceiver architecture

ABSTRACT

A transceiver, receiver, and transmitter are provided. The transmitter includes an in-phase path and a quadrature path, a first path associated with a first local frequency and a second path associated with a second local frequency, and a band selector for swapping the in-phase and quadrature paths to switch connection between the in-phase and quadrature paths and the first and second paths. The receiver includes an in-phase path and a quadrature path, a polyphase filter having first and second inputs and first and second outputs, and a selector for swapping the in-phase and quadrature paths to switch connection between the in-phase and quadrature paths and the first and second inputs. The transceiver may include a receiver and a transmitter, each of the receiver and the transmitter including in-phase signal and quadrature signal paths and first and second paths for processing signals on the in-phase signal and quadrature signal paths. In the transceiver, each of he receiver and the transmitter may include a band selector for selecting a band by swapping in-phase signal and quadrature signal paths. The transceiver may include a receiver, a transmitter, and a programmable matching block for impedance-matching between an antenna and the receiver input and between the antenna and the transmitter output. The receiver may include an in-phase path and a quadrature path, and a module provided for the in-phase path and the quadrature path for enhancing image rejection. The module includes a polyphase filter having first and second inputs and first and second outputs, and an adder for adding the first and second outputs.

FIELD OF INVENTION

The present invention relates to a transceiver, more specifically to acompact transceiver with a low-IF architecture.

BACKGROUND OF THE INVENTION

Wireless communications devices are used for a wide variety ofapplications, e.g., hearing aid, medical devices, In some of thewireless communications devices, a receiver uses a mixer for mixing asignal received from an antenna with a local oscillator (LO) signal. Themixer generates an IF (intermediate frequency) signal having a frequencyin a lower frequency band. However, by the mixing operation, image bandand desired band are translated into the same IF frequency. In order toremove the undesired frequency components, it is required to employ animage rejection mechanism in the receiver side.

FIG. 1 is a diagram illustrating a conventional 50 ohms and low-IFreceiver. The receiver 10 of FIG. 1 includes a matching block 12 coupledto a 50 ohms antenna 14 for receiving communication signals, a low noiseamplifier (LNA) 16, mixers 18 and 20, a 90° phase shifter 22 coupled tothe output of the mixer 20, and an adder 24 for adding the output fromthe mixer 18 and the output from the 90° phase shifter 22. The matchingblock 12 converts the receiver input impedance to 50 ohms to match thereceiver input to a 50 ohm conventional antenna. The receiver 10includes a band pass filter (BPF) 26 coupled to the output of the adder24, a limiting amplifier 28, and a demodulator 30 for recoveringinformation. The output from the LNA 16 is mixed with quadrature phasesof a local oscillator 40. Signals from two branches are added by theadder 24, then an undesired signal is cancelled.

The local oscillator block 40 includes a crystal oscillator 42, asynthesizer 44, and a 90° phase shifter 46. The local oscillator 40produces quadrature local oscillator signals 50 and 52 that are 90°phase shifted with respect to each other. The local oscillator signals50 and 52 are provided to the mixers 18 and 20, respectively.

FIG. 2 is a diagram illustrating another conventional 50 ohms and low-IFreceiver 60. In receiver 60, a polyphase filter 62 is provided to theoutputs of the mixers 18 and 20. One of the outputs from the polyphasefilter 62 is directly supplied to the BPF 26. The polyphase filter 62rejects the image signal and generates two wanted signal with 90 degreephase deference at the output. One of these signals can be connected tothe next stage.

Some improvements have been done to the receivers/transceiver in orderto reduce power consumption for portable devices. However currentlyavailable receivers/transceivers have still relatively high powerconsumption and large size.

There is a need to provide a low-power, compact image reject receiver,transmitter or transceiver having the receiver and the transmitter.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method and system thatobviates or mitigates at least one of the disadvantages of existingsystems.

According to an aspect of the present invention there is provided atransmitter, which includes an in-phase path and a quadrature path forconveying transmit data, a first path associated with a first localfrequency and a second path associated with a second local frequency;and a band selector for swapping the in-phase and quadrature paths toswitch connection between the in-phase and quadrature paths and thefirst and second paths.

According to another aspect of the present invention there is provided areceiver, which includes an in-phase path and a quadrature path forconveying received data, a polyphase filter having first and secondinputs and first and second outputs, and a selector for swapping thein-phase and quadrature paths to switch connection between the in-phaseand quadrature paths and the first and second inputs.

According to a further aspect of the present invention there is provideda transceiver, which includes a receiver and a transmitter. Each of thereceiver and the transmitter includes in-phase signal and quadraturesignal paths and first and second paths for processing signals on thein-phase signal and quadrature signal paths. Each of the receiver andthe transmitter includes a band selector for selecting a band byswapping in-phase signal and quadrature signal paths.

According to a further aspect of the present invention there is provideda transceiver, which includes a receiver, a transmitter, and aprogrammable matching block for impedance-matching between an antennaand the receiver input and between the antenna and the transmitteroutput.

According to a further aspect of the present invention there is provideda receiver, which includes an in-phase path and a quadrature path forconveying received data, and a module provided for the in-phase path andthe quadrature path for enhancing image rejection. The module includes apolyphase filter having first and second inputs and first and secondoutputs, and an adder for adding the first and 90 degree phase shiftedsignal of the second outputs.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will become more apparent fromthe following description in which reference is made to the appendeddrawings wherein:

FIG. 1 illustrates a conventional 50 ohms and low-IF receiver;

FIG. 2 illustrates another conventional 50 ohms and low-IF receiver;

FIG. 3 illustrates an example of a non-50 ohms transceiver having alow-IF transmitter and a low-IF image reject receiver in accordance withan embodiment of the present invention;

FIGS. 4A and 4B illustrate examples of the dual band operation of thetransceiver of FIG. 3;

FIG. 5 illustrates an example of the transceiver's operation in a firstfrequency band;

FIG. 6 illustrates an example of the transceiver's operation in a secondfrequency band;

FIG. 7 illustrates an example of the transmitter operation in the firstfrequency band;

FIG. 8 illustrates an example of the receiver operation in the firstfrequency band;

FIG. 9 illustrates an example of the transmitter operation in the secondfrequency band;

FIG. 10 illustrates an example of the receiver operation in the secondfrequency band;

FIG. 11 illustrates an example of the band select switch of FIG. 3;

FIG. 12 illustrates another example of the band select switch of FIG. 3;

FIG. 13 illustrates an example of creating 90 degree phase shift for thesecond stage of image rejection at the receiver side of FIG. 3;

FIG. 14A illustrates an example of the image rejection enhancement ofthe low-IF architecture by having two stages of image rejection inseries;

FIG. 14B illustrates the first stage image rejection of FIG. 14A;

FIG. 14C illustrates waveforms at the second stage image rejection ofFIG. 14A;

FIG. 15 illustrates another example of the low-IF image reject receiver;

FIG. 16A illustrates an example of the quadrature LO generation blockemployed in the transceiver of FIG. 3;

FIG. 16B illustrates another example of the quadrature LO generationblock employed in the transceiver of FIG. 3;

FIG. 16C illustrates a further example of the quadrature LO generationblock employed in the transceiver of FIG. 3;

FIG. 16D illustrates a further example of the quadrature LO generationblock employed in the transceiver of FIG. 3;

FIG. 17 illustrates a single port and non-50 ohms architecture for thetransceiver of FIG. 3 in accordance with an embodiment of the presentinvention;

FIG. 18 illustrates an example of the single port and non-50 ohmsarchitecture of FIG. 17 and the first stage of the receiver side and thelast stage of the transmitter;

FIG. 19A illustrates one examples of the programmable matching block ofFIG. 3;

FIG. 19B illustrates another examples of the programmable matching blockof FIG. 3;

FIG. 19C illustrates an example of an adjustable capacitive element ofFIG. 19A;

FIG. 20A illustrates an example of direct matching of a capacitiveantenna to a capacitive circuit; and

FIG. 20B illustrates an example of direct matching of an inductiveantenna to the capacitive circuit.

DETAILED DESCRIPTION

Embodiments of the present invention provide direct matched and ultralow power-compact transceiver architecture. The transceiver employs anultra low-IF architecture that can switch frequency bands by swappingin-phase and quadrature-phase paths and selecting a local oscillatorfrequency. The transceiver implements non-50 ohms direct matching of thetransceiver output and receiver input to an antenna. The transceiveralso employs image rejection enhancement technique. The transceiverarchitecture allows for ultra low power applications, enabling, forexample, audiology and other low power commutations solutions atmultiple carrier frequencies. Such applications may include, but notlimited to, wireless data device communications, audiology device(hearing aid etc.) communications, medical implantable devicecommunications.

FIG. 3 is a diagram illustrating an example of a transceiver inaccordance with an embodiment of the present invention. The transceiver100 of FIG. 3 includes a transmitter 102, a receiver 104, a localoscillator (LO) generator 106, and a programmable matching block 116.The transceiver 100 implements the dual band operation of thetransmitter 102 and the receiver 104.

The LO generator 106 includes, for example, a crystal oscillator 120, asynthesizer 122, and a 90° phase shifter 124. The LO generator 106 is aquadrature LO generator. The LO generator 106 produces low-IF localoscillator signals 126 and 128 that are 90 degree phase shifted withrespect to each other. The local oscillator signals 126 and 128 are usedin the transmitter 102 and the receiver 104. It is noted that theconfiguration of the LO generator 106 is not limited to that of FIG. 3.

The transmitter 102 includes a plurality of band-path filters (BPFs), aplurality of mixers corresponding to the plurality of BPFs. In FIG. 3,two BPFs 136 and 138 are shown as an example of the plurality of BPFs,and two mixers 140 and 142 are shown as an example of the plurality ofmixers. The transmitter 102 includes a band select switch 130 forselectively connecting an in-phase signal path 200 and a quadraturesignal path 202 to a first path 204 (the first output of the band selectswitch 130) and a second path 206 (the second output of the band selectswitch 130), respectively, or vice versa. The first path 204 is coupledto the BPF 136 and the mixer 140. The first path 206 is coupled to theBPF 138 and the mixer 142. The BPF 136, 138 rejects the harmonics andspurious of the applied signal to the band switch.

In the description, “204” may be used to represent the first output ofthe switch 130 or the path coupled to the mixer 140; “206” may be usedto represent the second output of the switch 130 or the path coupled tothe mixer 142.

The in-phase signal path 200 may be connected to the modulator 144through a digital/analog (D/A) converter 146. The quadrature signal path202 may be connected to the modulator 44 through a digital/analog (D/A)converter 148.

The in-phase signal path 200 and the quadrature signal path 202 transmitin-phase signals and quadrature signals output from a modulator 144,respectively. The path 200 includes a first signal line and a secondsignal line for transmitting which represent the differential operationof the transmitter. The path 202 includes a first signal line and asecond signal line for transmitting which represent the differentialoperation of the transmitter. The first path 204 includes a first signalline and a second signal line, corresponding to those of the path 200 or202. The second path 206 includes a first signal line and a secondsignal line, corresponding to those of the path 200 or 202.

One mixer 140 mixes the output from the BPF 136 with the localoscillator signal 128. The other mixer 142 mixes the output from the BPF138 with the local oscillator signal 126. The outputs of the mixers 140and 142 are supplied to an adder 150. The adder 150 is coupled to theprogrammable matching block 116 via a power amplifier (PA) 152.

The receiver 104 is a low-IF image reject receiver with a polyphasefilter 160 and power combiner after the polyphase filter 160. Thereceiver 104 includes a low noise amplifier (LNA) 162 and a plurality ofmixers. In FIG. 3, two mixers 164 and 166 are shown as an example of theplurality of mixers. The output from the programmable matching block 116is provided to the LNA 162. One mixer 164 mixes the output from the LNA162 with the local oscillator signal 126. The other mixer 166 mixes theoutput from the LNA 162 with the local oscillator signal 128.

The output of the mixer 164 includes a first signal line and a secondsignal line for transmitting which represent the differential operationof the receiver. The output of the mixer 166 includes a first signalline and a second signal line for transmitting which represent thedifferential operation of the receiver.

The receiver 104 includes a band select switch 168 having a first input208 coupled to the output of the mixer 164, a second input 210 coupledto the output of the mixer 166, a first output 212 coupled to the firstinput of the polyphase filter 160, and a second output 214 coupled tothe second input of the polyphase filter 160. The band select switch 160may be similar or the same as the band select switch 130. The output ofthe mixer 164 is selectively coupled to the first input 212 of thepolyphase filter 160 or the second input 214 of the polyphase filter 160while the output of the mixer 166 is selectively coupled to the secondinput 214 of the polyphase filter 160 or the first input 212 of thepolyphase filter 160.

In the description, “208” may be used to represent the first input ofthe switch 168 or the output of the mixer 164; “210” may be used torepresent the second input of the switch 168 or the output of the mixer166.

In the description, “212” may be used to represent the first output ofthe switch 168 or the first input of the polyphase filter 160; “214” maybe used to represent the second output of the switch 168 or the secondinput of the polyphase filter 160.

The first output of the polyphase filter 160 includes a first signalline and a second signal line for transmitting which represent thedifferential operation of the transmitter. The second output of thepolyphase filter 160 includes a first signal line and a second signalline for transmitting which represent the differential operation of thetransmitter. The first stage of image rejection is done by the polyphasefilter 160. However the image rejection of the polyphase filter 160 islimited to the mismatch between in-phase and quadrature-phase paths inthe layout. The second stage of the image rejection is done by creating90 phase shift 170 between the two paths after the polyphase filter 160and adding them at an adder 172 together.

The receiver 104 further includes a BPF 174 and an amplifier 176. Theoutputs 216 and 218 from the polyphase filter 160 and the 90 phaseshifter 170 are supplied to the adder 172. The output from the adder 172is filtered by the BPF 174 and amplified by the amplifier 176. Theamplifier 176 may be a variable gain amplifier or a limiting amplifier.

The output from the amplifier 176 is supplied to a demodulator 180. Thedemodulator 180 demodulates its input to derive information. Ananalog/digital (A/D) converter 182 may be located between the amplifier176 and the demodulator 180. Received Signal Strength Indicator (RSSI)184 is provided to the amplifier 176.

In transmit mode operation, the signals in the path 200 are filtered andthen mixed with the local oscillator signal 126 or 128 while the signalsin the path 202 are filtered and then mixed with the local oscillatorsignal 128 or 126. The frequency band for transmission is selectivelyswitched by swapping the paths 200 and 220, selecting the localoscillator signal or a combination thereof.

In receive mode operation, the signals output from the mixer 164 aresupplied to the first input 212 or the second input 214 of the polyphasefilter 160 while the signals output from the mixer 166 are supplied tothe second input 214 or the second input 212 of the polyphase filter160. The frequency band is selectively switched by swapping the paths208 and 210, selecting the local oscillator signal or a combinationthereof.

For example, the transceiver 100 may be used for a dual channel hearingaid communication that operates inside MICS band (402-405 MHz) andoutside MICS band (406-409MHz). In this example, one channel is selectedat 404 MHz in MICS band; the second channel is selected at 406 MHz; andthe local oscillator frequency is selected at 405 MHz. The bandselection is implemented by swapping in-phase and quadrature signals inthe transmitter 102 and the receiver 104.

The programmable matching block 116 couples the PA 152 and the LNA 162to the antenna 190. The programmable matching block 116 directly matchesthe PA 152 (transmitter output) to the antenna 190 in a transmit modeoperation and compensates for antenna impedance variations. Theprogrammable matching block 116 directly matches the LNA 162 (receiverinput) to the antenna 190 in a receive mode operation and compensatesfor antenna impedance variations. The antenna 190 may be a loop antennaor a dipole antenna.

FIGS. 4A and 4B are diagrams illustration examples of the dual bandoperation of the transceiver 100 of FIG. 3. In FIGS. 4A and 4B, “B1”represents one frequency band (frequency band 1); “B2” representsanother frequency band (frequency band 2).

In FIGS. 4A and 4B, “flo” represents a local oscillator frequency (e.g.,the output of the LO generator 106 of FIG. 1); “frfj” (j=1, 2, . . . ,n) represents desired channel frequency; “fimj” (j=1, 2, . . . , n)represents image channel frequency; and “fifj” (j=1, 2, . . . , n)represents intermediate frequency (IF) for different channels in casethe local oscillator is fixed for the selection of all channels. Anotheroption is to change the local oscillator frequency and keep theintermediate frequency fixed.

FIG. 4A shows an example of operation of a link between two sets of thetransceiver in FIG. 3 in band B1. In this link one set acts as atransmitter and the other set acts as a receiver and vice versa. FIG. 4Bshows an example of operation of a link between two sets of thetransceiver in FIG. 3 in band B2. Band selection is done by the bandselect switch.

FIG. 5 is a diagram illustrating an example of the transceiver'soperation in frequency band B1. In FIG. 5, two transceivers 100A and100B are shown. Each of the transceivers 100A and 100B corresponds tothe transceiver 100 of FIG. 3 and includes the transmitter 102 of FIG. 3and the receiver 104 of FIG. 3. In FIG. 5, the transceivers 100A and100B select frequency band B1 for communication.

Communication signals are transmitted from an antenna (e.g., 190 of FIG.3) coupled to the transceiver 100A. In the transceiver 100A, thereceiver is off (“RX: OFF”) and the transmitter is on (“TX: ON”). Thetransceiver 100A selects frequency band B1 for transmit mode operation.The transceiver 100B receives the communication signals from thetransceiver 100A through an antenna (e.g., 190 of FIG. 3) coupled to thetransceiver 100B. In the transceiver 100B, the transmitter is off (“TX:OFF”) and the receiver is on (“RX: ON”). The transceiver 100B selectsfrequency band B1 for receive mode operation.

FIG. 6 is a diagram illustrating an example of the transceiver'soperation in frequency band B2. In FIG. 6, the transceivers 100A and100B select frequency band B2 for communication.

Communication signals are transmitted from the transceiver 100A. In thetransceiver 100A, the receiver is off (“RX: OFF”) while the transmitteris on (“TX: ON”) and selects frequency band B2 for transmit modeoperation. The transceiver 100B receives the communication signals fromthe transceiver 100A. In the transceiver 100B, the transmitter is off(“TX: OFF”) while the receiver is on (“RX: ON”) and selects frequencyband B2 for receive mode operation.

FIG. 7 is a diagram illustrating an example of the transmitter operationin frequency band B1. In FIG. 7, the receiver side is not shown. In FIG.7, the synthesizer is not used.

The band select switch 130 includes switches SW1 and SW2. The switchesSW1 and SW2 are operated by a band select control signal. When frequencyband B1 is to be selected, the path 200 is coupled to the first output204 of the band select switch 130 by the switch SW1 while the path 202is coupled to the second output 206 of the band select switch 130 by theswitch SW2. The first output 204 is connected to the mixer 140. Thesecond output 206 is connected to the mixer 142. The mixer 140 utilizesthe local oscillator signal 126 while the mixer 142 utilizes the localoscillator signal 128.

Multiplication of IF and local oscillator signals and adding themtogether (150) at the output of two mixers 140 and 142 results:

AIF.Sin(ωIFt)xALO.Cos(ωLOt)−AIF.Cos(ωIFt)xALO.Sin(ωLOt)=−AIF.ALO.Sin((ωLO−ωIF)t).

“LO” represents Local Oscillator, and “IF” represents IntermediateFrequency. This indicates that the output signal is located at thefrequency of (ωLO-ωIF) which means the transmitter operates at band B1.

FIG. 8 is a diagram illustrating an example of the receiver operation infrequency band B1. In FIG. 8, the transmitter side is not shown.

The band select switch 168 includes switches SW3 and SW4. The switchesSW3 and SW4 are operated by a band select control signal. When frequencyband B1 is to be selected, the first input 212 of the polyphase filter160 is coupled to the mixer 164 by the switch SW3 while the second input214 of the polyphase filter 160 is coupled to the mixer 166 by theswitch SW4. The mixer 164 utilizes the local oscillator signal 126 whilethe mixer 166 utilizes the local oscillator signal 128.

The frequency response of the polyphase filter 160 depends on the phasedifference between its inputs. In this configuration the phase of signalline 208 leads the phase of signal line 210 by 90 degree. For thissituation signals at frequency band B1 will be passed through the filter174 and the signal at frequency band B2 will be rejected by the filter174.

FIG. 9 is a diagram illustrating an example of the transmitter operationin frequency band B2. In FIG. 9, the receiver side is not shown.

When frequency band B2 is to be selected, the in-phase signal path 200is coupled to the second output 206 of the band select switch 130 by theswitch SW1 while the quadrature signal path 202 is coupled to the firstoutput 204 of the band select switch 130 by the switch SW2.

Multiplication of IF and local oscillator signals and adding them (15)together at the output of two mixers 140 and 142 results:

AIF.Cos(ωIFt)xALO.Cos(ωLOt)−AIF.Sin(ωIFt)xALO.Sin(ωLOt)=AIF.ALO.Cos((ωLO+ωIF)t).

This indicates that the output signal is located at the frequency of(ωLO+ωIF) which means the transmitter operates at band B2.

FIG. 10 is a diagram illustrating an example of the receiver operationin frequency band B2. In FIG. 10, the transmitter side is not shown.

When frequency band B2 is to be selected, the first input 212 of thepolyphase filter 160 is coupled to the mixer 166 by the switch SW4 whilethe second input 214 of the polyphase filter 160 is coupled to the mixer164 by the switch SW3.

For this configuration the phase of signals to the input of thepolyphase filter 160 are swapped. Therefore frequency band B2 will bepassed through the filter 174 and frequency band B1 will be behaved asimage band and will be rejected.

FIG. 11 is a diagram illustrating an example of the band select switchof FIG. 1. The band select switch 220 of FIG. 11 corresponds to the bandselect switches 130 and 160 of FIG. 3. The band select switch 220includes a switch SW5 and a switch SW6. A band select control 222 isprovided to the band select switch 220. The band select control 222 isinverted by an inverter 224.

The switch SW5 connects inputs 230 a and 230 b to outputs 234 a and 234b and connects inputs 232 a and 232 b to outputs 236 a and 236 b, basedon the band select control 222. The switch SW5 includes switchtransistors 240 and 242 for connecting the inputs 230 a and 230 b to thefirst outputs 234 a and 234 b, and switch transistors 244 and 246 forconnecting the inputs 232 a and 232 b to the second outputs 236 a and236 b.

The switch SW6 connects the inputs 230 a and 230 b to the outputs 236 aand 236 b and connects the inputs 232 a and 232 b to the outputs 234 aand 234 b, based on the output of the inverter 224. The switch SW6includes switch transistors 248 and 250 for connecting the inputs 230 aand 230 b to the second outputs 236 a and 236 b, and switch transistors252 and 254 for connecting the inputs 232 a and 232 b to the firstoutputs 234 a and 234 b.

The inputs 230 a and 230 b correspond, for example, the two signal linesof the in-phase signal path 200 of FIG. 3. The inputs 232 a and 232 bcorrespond, for example, the two signal lines of the quadrature signalpath 202 of FIG. 3. The outputs 234 a and 234 b correspond, for example,the two signal lines of the path 204 of FIG. 3. The outputs 236 a and236 b correspond, for example, the two signal lines of the path 206 ofFIG. 3.

The inputs 230 a and 230 b correspond, for example, the two signal linesof the switch input 208 of FIG. 3. The inputs 232 a and 232 bcorrespond, for example, the two signal lines of the switch input 210.The outputs 234 a and 234 b correspond, for example, the two signallines of the polyphase filter input 212 of FIG. 3. The inputs 236 a and236 b correspond, for example, the two signal lines of the polyphasefilter input 214 of FIG. 3.

FIG. 12 is a diagram illustrating another example of the band selectswitch of FIG. 1. The band select switch 270 of FIG. 12 corresponds tothe band select switches 130 and 160 of FIG. 3. The band select switch270 includes a switch SW7 and a switch SW8. A band select control 222 isprovided to the band select switch 270. The band select control 222 isinverted by the inverter 224.

The switch SW7 operates on the first outputs 234 a and 234 b based onthe inputs 230 a and 230 b and the band select control 222. The switchSW7 operates on the second outputs 236 a and 236 b based on the inputs232 a and 232 b and the band select control 222. The switch SW7 includesswitch transistors 272 and 274 and a current source 276, and switchtransistors 278 and 280 and a current source 282. By turning the currentsource on or off the two transistors act as a differential switch whichis on or off.

The switch SW8 operates on the second outputs 236 a and 236 b based onthe inputs 230 a and 230 b and the output from the inverter 224. Theswitch SW8 operates on the first outputs 234 a and 234 b based on theinputs 232 a and 232 b and the output from the inverter 224. The switchSW8 includes switch transistors 284 and 286 and a current source 288,and switch transistors 290 and 292 and a current source 294.

FIG. 13 is an example of a diagram illustrating implementation of the 90degree phase shift for the second stage of image rejection at thereceiver side 104 of FIG. 3. The left side of FIG. 13 illustrates therelationship among the output from the polyphase filter 160, the shifter170 and the adder 172. The right side of FIG. 13 illustrates an exampleof a path from the output of the polyphase filter 160 to the adder 172.Image rejection is enhanced by combination of two image rejectiontechniques. The first stage of image rejection is done by the polyphasefilter 160. The next stage of image rejection includes 90 degree-phaseshift path 186 and the adder 172, and is done by adding 90 degree phaseshift (170) at the output of one of the polyphase filter's path andadding the two paths together (172).

FIG. 14A illustrates an example of the image rejection enhancement ofthe low_IF architecture with two stages of image rejection. As shown inFIG. 14A, the image rejection is performed by a first stage imagerejection including a polyphase filter 160A, and a second stage imagerejection including the 90 degree-phase shift path 186 and the adder172. The polyphase filter 160A is one example of the polyphase filter160 of FIG. 3. FIG. 14B illustrates image rejection by the first stageimage rejection 160A in FIG. 14A. FIG. 14C illustrates image rejectionby the second stage image rejection in FIG. 14A.

FIG. 15 is a diagram illustrating another example of the low-IF imagereject receiver of FIG. 3. The low-IF image reject receiver 340 of FIG.15 is also usable in the receiver side of the transceiver 100 of FIG. 3.The receiver 340 includes the mixers 164, 166, the polyphase filter 160,and the adder 172. The switch 168 may be provided between the mixers 164and 166 and the polyphase filter 160.

FIGS. 16A-16D are diagrams illustrating the examples of a quadrature LOgeneration block employed in the transceiver of FIG. 1. Each of thequadrature LO generation block 400, 410, 430 and 440 of FIGS. 16A-16D isusable as the LO generator 106 of FIG. 3 and provides the quadraturelocal oscillator signals 126 and 128 of FIG. 3.

Referring to FIG. 16A, the quadrature LO generation block 400 includes avoltage control oscillator (VCO) 402 for providing a signal with 810MHz, a LO buffer 404 and a quadrature signal generator 406 for providingin-phase and quadrature signals with 405 MHz. The 810 MHz VCO 402 isbuffered (404) and is divided by 2 by the quadrature generator divider406.

Referring to FIG. 16B, the quadrature LO generation block 410 includes aVCO 412 for providing a signal with 405 MHz, a LO buffer 414, an RCpolyphase block 416 for providing in-phase and quadrature signals and LObuffers 418 and 420 for the in-phase and quadrature signals. The 405 MHzVCO 412 is buffered (414) and quadrature LO signals are generated by thepolyphase filter 412 and the buffered (418, 420) again after polyphasefilter 412.

Referring to FIG. 16C, the quadrature LO generation block 430 includes across coupled quadrature VCO 432 for providing in-phase and quadraturesignals with 405 MHz, a LO buffer 434 for the in-phase and quadraturesignal, and a LO buffer 436 for the quadrature signal. In thisconfiguration, the two oscillator will be coupled to each other togenerate quadrature local oscillator 432.

Referring to FIG. 16D, the quadrature LO generation block 440 includes aVCO 442 for providing a signal with 270 MHz, a buffer 444, a quadraturesignal generator 446 for providing in-phase and quadrature signals with135 MHz, a mixer 448 for mixing the output from the buffer 444 with thein-phase signal and a mixer 450 for mixing the output from the buffer444 with the quadrature signal. The 270 MHz VCO 442 is buffered (444)and divided by the quadrature divider 446 to generate quadrature LOsignals. Then 135 MHz quadrature signals are mixed with the 270 MHz VCO448, 450 to generate 400 MHz quadrature local oscillator.

FIG. 17 is a diagram illustrating an example of a single port connectionfor the programmable matching block 116 of FIG. 3 in accordance with anembodiment of the invention. In FIG. 17, “300” represents a single portconnection to an antenna (e.g., 190 of FIG. 3). FIG. 18 is a diagramillustrating an example of the single port and non-50 ohms architectureof FIG. 17 and the first stage of the receiver side and the last stageof the transmitter. In FIG. 18, “302” represents one example of a firststage of the LNA (e.g., 162 of FIG. 3) in the receiver side and “304”represents one example of a last stage of the PA (e.g., 152 of FIG. 3)in the transmitter side. The antenna connected to the programmablematching block 116 is a single port antenna.

Referring to FIGS. 17-18, the port 300 includes connectors 310 a and 310b that communicate with the in-phase signal path and the quadraturesignal path of the transceiver side. The antenna includes connectors 312a and 312 b that are connectable to the connectors 312 a and 312 b.

In FIG. 18, “Zrx” represents the impedance of the receiver input, and“Ztx” represents the required impedance at the transmitter output. InFIG. 18, “Zant” represents the impedance of the antenna. In receivemode, the programmable matching block 116 directly matches “Zrx” to“Zant” and compensates for the variation of the antenna impedance“Zant”. In transmit mode, the programmable matching block 116 directlymatches “Zant” to required “Zant” and also compensates for the variationof the antenna impedance “Zant”.

The programmable matching block is designed in such a way to transforminput impedance of the transceiver in receive mode to the antennaimpedance and also transform the antenna impedance to the requiredimpedance at the output of the transceiver in transmit mode. As anexample for operation of the transceiver at 400 MHz band the requiredoutput impedance at the transmitter output is 8K ohm to deliver acertain power. Therefore the impedance of a non-50 ohm antenna istransformed to an 8K ohm at the transmitter output. On the receiver sidethe input impedance of the receiver is transformed to conjugateimpedance of the non-50 ohm antenna. The programmable matching blockaccommodate the required transformation on both directions and alsocompensate for the variation in antenna impedance due to change inantenna environment. By applying this matching technique and usingprogrammable matching circuit the required matching circuit foroperation in transmit and receive mode can be shared. Therefore there isno need for two antennas or external switch for transmit and receiveoperation. The conventional design matches the receiver input to 50 ohmor transforms 50 ohm antenna to required impedance at the transmitteroutput and connect a 50 ohm antenna to the transceiver. Also twodifferent matching circuits or external switch is required for operatingin transmit or receive mode. This is not efficient for ultra low powerapplications because part of signal power will be lost in extra matchingcomponents required for matching to 50 ohm and extra off-chip componentsare required. The programmable matching block 116 compensate forvariation in antenna impedance by monitoring RSSI signal and keeps theantenna and front-end in match condition. This mechanism saves thetransceiver power and have maximum power transfer between antenna andcircuit, especially for ultra low power transceivers (e.g., 100 of FIG.3).

The transmitter 102 and the receiver 104, and a switch for switching thetransmit and receive modes may be on chip. No off-chip switching isrequired for switching between transmit and receive modes.

FIGS. 19A-19B illustrate examples of the programmable matching block ofFIG. 3. In one example, the programmable matching block 116 of FIG. 3may include a component 116 a of FIG. 19A (referred to as programmablematching block 116 a). In another example, the programmable matchingblock 116 of FIG. 3 may include a component 116 b of FIG. 19B (referredto as programmable matching block 116 b).

Referring to FIGS. 19A-19B, each of the programmable matching blocks 116a and 116 b includes the connections 310 a and 310 b for communicatingwith an antenna (e.g., 190 of FIG. 3) and connections 314 a and 314 bfor communicating with the PA 152 and LNA 162 of FIG. 3. Each of theprogrammable matching blocks 116 a and 116 b may be a module and bedetachably connectable to the PA and LNA via 314 a and 314 b.

The programmable matching block 116 a includes adjustable capacitiveelement 500. The programmable matching block 116 b includes adjustablecapacitive elements 502 and 504, each of which includes adjustablecapacitance.

FIG. 19C illustrates an example of the adjustable capacitive element500. The adjustable capacitive element 500 a of FIG. 19C includes aplurality of capacitors 510 a, 510 b, 510 c, and 510 d and a pluralityof transistors 512 a, 512 b, 512 c, and 512 d. The capacitors 510 a, 510b, 510 c, and 510 d have capacitance C0, C1, C2, C4, respectively. Thetransistors 512 a, 512 b, 512 c, and 512 d have gate terminals forreceiving control signals B0, B1, B2, and B3, respectively. The controlsignals B0, B1, B2, and B3 are determined by, for example, RSSI. Inresponse to the control signals B0, B1, B2, and B3, the capacitance ofthe element 500 a is determined. The adjustable capacitive element 502,504 of FIG. 19B may have structure similar to the adjustable capacitiveelement 500 a of FIG. 19C.

In cases that antenna environment changes the antenna impedance changes.As an example when the antenna is close to human body or human head incase of hearing aid application the antenna impedance changes compare tothe situation that antenna is in free space. The programmable matchingcircuit matches the new antenna impedance in new environment to thetransmit output or receive input impedance. The variable element in theprogrammable matching circuit is at least one or two capacitors that canbe changed digitally by a number of digital bits. The resolution of theprogrammability depends on the number of bits that are used to controlthe capacitance.

It is well understood by one of ordinary skill in the art that thecomponents 116A, 116B and 116C of FIGS. 19A-19C are examples only. Theprogrammable matching block 116 of FIG. 3 may include programmableadjustable inductive elements.

FIGS. 20A and 20B illustrate examples of direct matching of a capacitiveantenna and an inductive antenna to a capacitive circuit, respectively.In FIGS. 20A and 20B, “520” represents a conductive circuit. Theconductive circuit 520 may be, the first stage of the receiver 104 ofFIG. 3, or the last stage of the transmitter 102 of FIG. 3. In FIG. 20A,“522” represents a capacitive antenna which is an example of the antennaattached to the transceiver 100 of FIG. 3. In FIG. 20A, “524” showsdirect matching of the capacitive antenna 522 to the capacitive circuit520 through the programmable matching block (116) having an adjustableinductive element 526. In FIG. 20B, “532” represents an inductiveantenna which is an example of the antenna attached to the transceiver100 of FIG. 3. In FIG. 20B, “534” shows direct matching of the inductiveantenna 532 to the capacitive circuit 520 through the programmablematching block (116) having an adjustable capacitive element 536.

One or more currently preferred embodiments have been described by wayof example. It will be apparent to persons skilled in the art that anumber of variations and modifications can be made without departingfrom the scope of the invention as defined in the claims.

1. A transmitter comprising: an in-phase path and a quadrature pathconveying transmit data; a first path associated with a first localfrequency and a second path associated with a second local frequency;and a band selector swapping the in-phase and quadrature paths to switchconnection between the in-phase and quadrature paths and the first andsecond paths.
 2. A transmitter as claimed in claim 1, wherein the bandselector comprises at least one of: a switch for connecting, based on aband select signal, one of the in-phase and quadrature paths to thefirst path having a first mixer for mixing a first local oscillatorsignal and the other to the second path having a second mixer for mixinga second local oscillator signal; a module for changing the first andsecond local frequencies; and a module for changing intermediatefrequency of the transmit data.
 3. A receiver comprising: an in-phasepath and a quadrature path conveying received data; a polyphase filterhaving first and second inputs and first and second outputs; and aselector swapping the in-phase and quadrature paths to switch connectionbetween the in-phase and quadrature paths and the first and secondinputs.
 4. A receiver as claimed in claim 3, wherein the selectorcomprises at least one of: a switch for connecting, based on a bandselect signal, one of the in-phase and quadrature paths to the firstinput and the other to the second input; an adder for adding a signalfrom the first output and a signal from the second output; and a modulefor enhancing image rejection.
 5. A receiver as claimed in claim 4,wherein the module comprises: a phase shifter provided between the firstoutput and the adder for phase-shifting a signal on the first output. 6.A receiver as claimed in claim 3, wherein the in-phase path comprises: afirst mixer for mixing a first local oscillator signal, and wherein thequadrature path comprises: a second mixer for mixing a second localoscillator signal.
 7. A receiver as claimed in claim 6, furthercomprising: a module for changing the first and second local oscillatorsignals.
 8. A receiver as claimed in claim 3, wherein the selectorcomprises: a phase shifter for phase-shifting a signal on the firstoutput; and an adder for adding a signal on the second output and asignal output from the phase shifter.
 9. A transceiver comprising: thetransmitter as claimed in claim 1; and a receiver including: an in-phasereceive path and a quadrature receive path conveying received data; anda selector swapping the in-phase receive and quadrature receive paths toswitch connection between the in-phase receive and quadrature receivepaths.
 10. A transceiver as claimed in claim 9, wherein the bandselector of the transmitter comprises: a switch for connecting, based ona band select signal, one of the in-phase and quadrature paths of thetransmitter to the first path having a first mixer for mixing a firstlocal oscillator signal and the other to the second path having a secondmixer for mixing a second local oscillator signal.
 11. A transceiver asclaimed in claim 9, wherein the receiver comprises: a polyphase filterincluding a first input, a second input, a first output and a secondoutput, and wherein the selector of the receiver comprises: a switch forconnecting, based on a band select signal, one of the in-phase andquadrature receive paths to the first input and the other to the secondinput of the polyphase filter.
 12. A transceiver as claimed in claim 9,further comprising: a module for switching a receive mode for operatingthe receiver and a transmit mode for operating the transmitter.
 13. Atransceiver comprising: a receiver; a transmitter; and a programmablematching block compensating for antenna impedance variation due toenvironment change and implementing impedance-matching between anantenna and the receiver input and between the antenna and thetransmitter output through a shared matching circuit block.
 14. Atransceiver as claimed in claim 13, wherein the programmable matchingblock is detachably connectable to the antenna.
 15. A transceiver asclaimed in claim 14, wherein the programmable matching block isdetachably connectable to the antenna via a single port.
 16. Atransceiver as claimed in claim 13, wherein the programmable matchingblock comprises at least one of: a programmable inductor; and aprogrammable capacitor.
 17. A receiver comprising: an in-phase path anda quadrature path conveying received data; and a module provided for thein-phase path and the quadrature path, enhancing image rejection, themodule including: a polyphase filter having first and second inputs andfirst and second outputs; and an adder adding the first and secondoutputs.
 18. A receiver as claimed in claim 17, wherein the modulecomprises: a phase shifter provided between the polyphase shifter andadder for phase-shifting a signal on the first output.